The present invention relates to integrated extracorporeal oxygenation and pumping systems having an integrated heat exchanger.
Each year hundreds of thousands of people are afflicted with vascular diseases, such as arteriosclerosis, that result in cardiac ischemia. For more than thirty years, such disease, especially of the coronary arteries, has been treated using open surgical procedures, such as coronary artery bypass grafting. During such bypass grafting procedures, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass, and the heart is stopped using a cardioplegia solution.
Recently, the development of minimally invasive techniques for cardiac bypass grafting, for example, by Heartport, Inc., Redwood City, Calif., and CardioThoracic Systems, Inc., Cupertino, Calif., have placed a premium on reducing the size of equipment employed in the sterile field. Whereas open surgical techniques typically provide a relatively large surgical site that the surgeon views directly, minimally invasive techniques require the placement of endoscopes, video monitors, and various positioning systems for the instruments. These devices crowd the sterile field and can limit the surgeon""s ability to maneuver.
At the same time, however, the need to reduce priming volume of the oxygenator and pump, and the desire to reduce blood contact with non-native surfaces has increased interest in locating the oxygenator and pump as near as possible to the patient.
In recognition of the foregoing issues, some previously known cardiopulmonary systems have attempted to miniaturize and integrate certain components of cardiopulmonary systems. U.S. Pat. Nos. 5,266,265 and 5,270,005, both to Raible, describe an extracorporeal blood oxygenation system having an integrated blood reservoir, an oxygenator formed from a static array of hollow fibers, a heat exchanger, a pump and a pump motor that is controlled by cable connected to a control console.
The systems described in the foregoing patents employ relatively short flow paths that may lead to inadequate gas exchange, due to the development of laminar flow zones adjacent to the hollow fibers. U.S. Pat. No. 5,411,706 to Hubbard et al. describes one solution providing a longer flow path by recirculating blood through the fiber bundle at a higher flow rate than the rate at which blood is delivered to the patient. U.S. Pat. No. 3,674,440 to Kitrilakis and U.S. Pat. No. 3,841,837 to Kitrilakis et al. describe oxygenators wherein the gas transfer surfaces form an active element that stirs the blood to prevent the buildup of boundary layers around the gas transfer surfaces.
Makarewicz et al., xe2x80x9cNew Design for a Pumping Artificial Lung,xe2x80x9d ASAIO Journal, 42(5):M615-M619 (1996), describes an integrated pump/oxygenator having a hollow fiber bundle that is potted between an inlet gas manifold and an outlet gas manifold. The fiber bundle is rotated at high speed to provide pumping action, while oxygen flowing through the fiber bundle oxygenates the blood. Like the device described in Ratan et al., xe2x80x9cExperimental evaluation of a rotating membrane oxygenator,xe2x80x9d J. Thoracic and Cardio. Sura., 53(4):519-526 (1967), a separate heat exchanger must be used for cooling the blood.
U.S. Pat. No. 5,830,370 to Maloney et al. describes a device having a fiber bundle mounted for rotation between a fixed central diffuser element and an outer wall of a housing. The fiber bundle is rotated at speeds sufficiently high to cause shear forces that induce turbulent flow within the blood. Rotation of the fiber bundle is also used to augment heat exchange between the blood and a coolant surrounding a portion of the blood reservoir. The limited heat transfer surface area provided in such designs, however, may be insufficient to provide adequate cooling.
Other patents for systems having stationary fiber bundles also have addressed the role of the heat exchanger in an integrated assembly. For example, U.S. Pat. No. 3,768,977 to Brumfield et al. describes a blood oxygenator in which gas exchange and temperature regulation occur in the same chamber to reduce the risk of gas bubble evolution and gas embolism stemming from elevated blood temperatures. U.S. Pat. No. 4,791,054 to Hamada et al. describes an integrated heat exchanger and blood oxygenator that uses hollow fibers, formed of an organic material, as the heat transfer tubes. U.S. Pat. No. 5,770,149 to Raible et al. describes an integrated blood pump, heat exchanger, and membrane oxygenator in which heat exchange occurs after pumping but before oxygenation.
Although the devices having rotating fiber bundles described in the foregoing references offer some desirable features, such as low priming volume and low surface area, it is unclear whether such devices can provide adequate heat exchange capability, due to either limited heat transfer area or inadequate pump head to provide flow through a separate heat exchanger over a wide range of flow rates.
In view of the foregoing, it would be desirable to provide an integrated extracorporeal blood oxygenator, pump and heat exchanger having a rotating fiber bundle that provides compact size, low priming volume, low surface area and adequate temperature regulation.
It also would be desirable to provide an integrated extracorporeal blood oxygenator, pump and heat exchanger with a hollow fiber bundle having a rotating fiber bundle, and also providing adequate heat transfer area between the blood and the coolant to facilitate regulation of the blood temperature.
It further would be desirable to provide an integrated extracorporeal blood oxygenator, pump and heat exchanger having a rotating hollow fiber bundle that provides adequate pump head to account for pressure head losses in the heat exchanger over a wide range of blood flow rates.
In view of the foregoing, it is an object of the present invention to provide an integrated extracorporeal blood oxygenator, pump and heat exchanger having a rotating fiber bundle that provides compact size, low priming volume, low surface area and adequate temperature regulation.
It is another object of the present invention to provide an extracorporeal blood oxygenator, pump and heat exchanger with a hollow fiber bundle having a rotating fiber bundle and also having adequate heat transfer area between the blood and the coolant to facilitate regulation of the blood temperature.
It is yet another object of this invention to provide an integrated extracorporeal blood oxygenator, pump and heat exchanger having a rotating hollow fiber bundle that provides adequate pump head to account for pressure head losses in the heat exchanger over a wide range of blood flow rates.
These and other objects of the invention are accomplished by providing an integrated extracorporeal blood oxygenator, pump and heat exchanger, suitable for use within a sterile field, that has a low priming volume and low surface area. In accordance with the principles of the present invention, the oxygenator, pump and heat exchanger system includes a rotating hollow fiber bundle assembly that both oxygenates the blood and develops sufficient pressure head to pump the blood through an integral heat exchanger in fluid communication with the blood flow path. In addition, heat exchanger has a compact size but provides sufficient heat transfer area to facilitate temperature regulation of blood flowing through the device.
In one preferred embodiment, the heat exchanger comprises a metal waffle-like wall disposed in a separate compartment of the housing, so that blood passes along one side of the wall while coolant passes along the opposite side of the wall. In an alternative embodiment, the heat exchanger comprises a stationary bundle of non-permeable hollow fibers through which blood flows, while a coolant passes along the exterior of the bundle.
In yet another alternative embodiment, the heat exchanger comprises a coiled metal tube disposed in a housing between the rotating fiber bundle and the housing wall. Coolant passes through an interior lumen of the coiled tube to absorb heat from (or alternatively, transfer heat to) blood passing along the exterior of the rotating fiber bundle.
Methods of using the integrated system of the present invention are also provided.